Research

The members of SAWLab Saxony comprise scientists and technologists from IFW, different research institutions and industrial partners. Therewith our activities and competences span all topics related to acoustoelectronics: fundamentals, electrode and substrate materials, advanced thin film technologies and specific devices and acoustoelectronic applications.

The most important research and development topics cover:

Selected Results:

Fundamentals

Higher-order effects in tSAW-actuated microfluidic channels

The use of high-frequency surface acoustic waves (SAW) underpin an exciting range of promising techniques for non-contact manipulation of fluid and objects at micron scale (e.g. particles, cells and biomolecules). The development of state-of-the-art SAW-driven technologies, however, require an in depth understanding of the various phenomena that takes place in such systems. Through numerical and experimental investigation, we have identified five distinct mechanisms that arise due to incidence of a travelling SAW through a microfluidic channel. These include migration of particles along the TSAW propagation direction, periodic patterning of particles along two directions and fluid swirling in two orthogonal planes. 

A. Fakhfouri, C. Devendran, T. Albrecht, D. J. Collins, A. Winkler, H. Schmidt, A. Neild, Lab on a Chip 18, 2214-2224 (2018), URL.

Functional Thin Films

RuAl as metallization for high temperature SAW devices

RuAl is a material which is investigated for high temperature thin film applications due to its promising high temperature properties. RuAl thin films are co-sputtered from elemental targets and the films are annealed at temperatures up to 800 °C under high vacuum and afterwards characterized concerning the RuAl phase formation, film morphology, local and global chemical composition and electrical resistivity. The investigation of these films on thermally oxidized Si substrates as well as on high temperature stable La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) substrates shows a stability of these films after annealing at 800 °C for 10 h in high vacuum. In the case of LGS and CTGS the application of a SiO2 barrier layer between substrate and RuAl film is necessary because of O and Ga diffusion out of these substrates.  

M. Seifert, S.B. Menzel, G.K. Rane, M. Hoffmann, T. Gemming, Materials Research Express 2, 085001 (2015), URL.
M. Seifert, G.K. Rane, B. Kirbus, S. Menzel, T. Gemming, Materials 8, 8868-8876 (2015), URL.
M. Seifert, G.K. Rane, S. Menzel, T. Gemming, Journal of Alloys and Compounds 684, 510-517 (2016), URL.
M. Seifert, G.K. Rane, S. Menzel, T. Gemming, Journal of Alloys and Compounds 688, 228-240 (2016), URL.

Microstructural characterization of thin film systems for SAW based high-temperature sensors

High-temperature stable material systems for SAW interdigital transducers based on refractory metals tungsten and molybdenum are studied. In-depth microstructural characterization of these thin films is performed in order to tailor their properties as per requirement. Analysis methods include thin film X-ray diffraction, scanning and transmission electron microscopy, Auger electron spectroscopy, X-ray texture and X-ray reflectivity measurements, and atomic force microscopy. The thermal stability of the film systems on special high-temperature stable piezoelectric substrates such as La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) is investigated up to 800 °C.   

G.K. Rane, S. Menzel, T. Gemming, J. Eckert, Thin Solid Films 571, Part A: 1-8 (2014), URL.

Substrate Materials

Elastic and dielectric properties of Langasite family crystals at low temperatures

Elastic and dielectric properties of La3Ga5SiO14 (LGS) and Sr3NbGa3Si2O14 (SNGS) piezoelectric crystals were studied at temperatures from 4.2 K to 300 K. The obtained results for the elastic constants (with the exception of C66 for LGS) are treated using Varshni approach based on the Einstein oscillator model. In LGS, the elastic constant C66 versus temperature shows a turnover point close to room temperature followed by a gradual decreasing with decreasing temperature down to 4.2K. It is also demonstrated, that high piezoelectric activity of the crystals keeps down to 4.2K which predestines clearly LGS and SNGS as promising materials for possible applications at cryogenic temperatures.

[1] A.V. Sotnikov, E.P. Smirnova, H. Schmidt, M. Weihnacht, Phys. Solid State 57 (2015) No.6, 1183-1187, URL.
[2] A. Sotnikov, E. Smirnova, H. Schmidt, M.Weihnacht, J. Götze, S. Sakharov, Prodeedings of the 2015 Joint IEEE International Frequency Control Symposium and European Frequency and Time Forum, Denver, USA, p106-110 (2015), URL.

Advanced technology

Advanced metallization concepts including metallic glasses

Thin film metallic glasses (TFMG) possess a number of advantageous properties for IDT electrode materials compared with crystalline thin films. Due to the lack of lattice defects like grain boundaries or dislocations a high strength and toughness are achieved. Furthermore an extremely low surface roughness of amorphous films and missing fast diffusion paths with low activation energy as observed for grain boundaries can push TFMG into specific applications for acoustoelectronics. We developed the expertise for preparing and characterization of several TFMG in a wide composition range of binary alloys through two-source dc magnetron sputtering. Microstructure of polycrystalline Ni (left) and amorphous Ni-Zr thin film (right). Contrary to the NiZr-film the microstructure of the pure Ni exhibits grain boundaries of different angle measured by EBSD.

H. Turnow, H. Wendrock, S. Menzel, T. Gemming, J. Eckert: Synthesis and Characterization of Amorphous Ni–Zr Thin Films, Thin Solid Films, 561C (2014): 48-52, URL.

Devices and Applications

Compact SAW aerosol generator

We demonstrate a compact SAW-based aerosol generator amenable to mass production fabricated using simple techniques including photolithography, computerized numerical control (CNC) milling and printed circuit board (PCB) manufacturing. Using this device, we present comprehensive experimental results exploring the complexity of the acoustic atomization process and the influence of fluid supply position and geometry, SAW power and fluid flow rate on the device functionality. These factors in turn influence the droplet size distribution, measured here, that is important for applications including liquid chromatography, pulmonary therapies, thin film deposition and olfactory displays.

Winkler, A.; Harazim, S. M.; Collins, D. J.; Brünig, R.; Schmidt, H.; Menzel, S. B.: „Compact SAW aerosol generator”, Biomed Microdev 19,1 (2017), URL.
Winkler, A.; Harazim, S. M.; Menzel, S. B.; Schmidt, H.: „SAW-based fluid atomization using mass-producible chip devices”, Lab Chip 15, 3793-3799 (2015), URL.

 

Local temperature determination at the SAW chip surface using Raman spectroscopy and thermography

The temperature at the surface of surface acoustic wave (SAW) devices is a critical parameter not only for their design but also for the understanding of failure mechanisms like acoustomigration. Conventional techniques such as thermocouples cannot be used to determine the local temperature in the micrometer range within the aperture area due to their effect on SAW propagation. We introduced contactless methods based on the intensity ratio of Stokes- and Anti-Stokes lines of Raman spectra as well as on thermography for a very local temperature determination also applicable inside of the aperture area of the interdigital transducers.

M. Spindler, B. Uhlig, S. Menzel, C. Huck and T. Gemming, J. Appl. Phys. 114, 164317 (2013), URL.

Thin Film Analytics

ARXPS Box – The advanced software for ARXPS analysis

Thin film analysis done by angle-resolved X-Ray Photoelectron Spectroscopy is in need for sophisticated model calculations that provide the correct layer structure based on the XPS data of the specimen.
We therefore developed an easy to handle software based on profound Matlab™ algorithms that allows a broad adjustment of any layer parameter and excellent computation. Using the one-click procedure the user is able to evaluate various best fit solutions. The great usability of the ARXPS Box is completed by multiple data and graphic export functions.

U. Vogel, T. Gemming, J. Eckert, S. Oswald, Surf Interface Anal 46 (2014) p.1033, URL.